A conventional archery bow (FIG. 1) converts the mechanical work of drawing the bowstring into potential energy stored in the spring tension of the limbs which is released as the kinetic energy of the arrow. According to the laws of physics the work input, stored potential energy, and released kinetic energy are equivalent except for frictional and dynamic losses.
The energy capacity of the traditional bow, shown in FIGS. 1 and 2, is the product of the draw-weight and power-stroke. The power-stroke is the draw-length minus the brace-height (FIG. 2). In the design of the traditional bow, the brace-height provides clearance for the gripping hand by limiting the forward travel of the bowstring to a distance from the grip. The usable draw-weight is limited by the strength of the archer, the draw-length is limited by the reach of the archer, and the power-stroke is reduced by the brace-height. These three factors are the primary limitations to the energy capacity of the traditional bow.
The inverted bow (FIG. 3) requires less string and limb-tension for a given draw-weight and power-stroke compared to the traditional bow, but stores and releases no more energy. The inverted bow is inherently problematic to grasp and hold due to rotational forces about the grip, lacks practical methods to nock and rest the arrow, and limits the draw-length by the dimensions of the bow. For these reasons, the inverted bow has never come into practical use.
The compound bow (FIG. 4) utilizes an eccentric cam system to modify the draw-force versus draw-length characteristics of the bow, and to provide a substantial reduction of draw-weight at the full-draw position. As in the case of the traditional bow, the power-stroke is reduced by the brace-height and the compound bow is subject to the same factors which limit energy capacity.